1. Field of the Invention
The present invention relates to plates based on acrylic polymers to be used as barriers having antinoise and antifragmentation properties.
In particular it relates to transparent polymethylmethacrylate plates having a high thickness, in the range of 12-25 mm, preferably 15-20 mm, for motorway barriers, viaducts, bridges, etc.
2. Description of the Related Art
It is well known to utilize acrylic panels rather than other materials in the construction of antinoise barriers, to be utilized in motorway.
The technical problem arises when a blunt instrument crashes into the panel thus determining the formation of fragments which fall in the road area.
The same problem arises in case of viaducts and bridges causing danger situations for what is situated under these structures.
It is known to build protective barriers against this fragmentation by means of nets wrapping the panel. However the net meshes must have wide sizes otherwise the panel does not show any more transparence phenomena, necessary for the practical applications of these panels. The alternative utilized in practice consists in employing nets with large meshes to allow a certain transparence. The drawback of this technical solution resides in that the antifragmentation of the net results in this way very reduced. Moreover, to maintain a certain transparence, panels must be subject to very frequent cleaning operations since nets favor the accumulation of substances lowering the transparence, for instance dust, leaves, etc. This requires the taking down of nets with the consequent increase of maintenance costs.
The same drawbacks as regards the transparence occur even though nets are inserted into the panel, even if in this way the cleaning operation described above is eliminated.
From patent U.S. Pat. No. 5,040,352, transparent antifragmentation panels based on acrylic resins are knwon, which contain about in the middle of the panel threads, fibers, bands and nets of plastic material. In particular the materials indicated as suitable for the reinforcement of acrylic panels are monofilaments of polyamide or polypropylene due to their poor adhesion to the acrylic glass.
The preferred sizes for monofilaments are 0.2-2 mm of diameter. The preferred sizes for plastic bands which can consist of films or fibers, have a width from 5 to 25 mm and a thickness from 0.2 to 2 mm.
The distance between the filaments or the bands must be in the range from 10 to 100 mm.
The advantage of these plastic materials inserted about in the middle of the panel is due to the fact that they are transparent enough and therefore reduce the problems of reduced transparence with respect to the art and avoid the cleaning operations due to the environmental pollution being inside the panel. The antifragmentation properties result good.
The teaching of said patent is very precise as to the placing of threads in manufactured articles, in addition to the size, the threads direction which can be perpendicular or forming an angle different from 90.degree.. Both the description and the exemplifying part point out that threads must be inserted about in the middle of the thickness of the panel.